Optimising production and long-term bulk storage of hydrogen from offshore wind in subsurface salt caverns

There is growing interest in large-scale energy storage using green hydrogen produced from renewable sources such as offshore wind energy. This is being driven by a desire for energy security; the push towards zero‑carbon electricity; and the need for back-up power to complement variable renewables. Storing hydrogen in subsurface caverns has several advantages: the offshore location minimises impacts on land-based communities and infrastructure; the large potential volumes are suitable for long-duration energy storage; and the technology is modular and scalable. There are several locations around the world with plentiful wind resources adjacent to geological features such as salt caverns or depleted gas fields suitable for subsurface storage of hydrogen. The Kish Basin of the Irish Sea is one such location, with several major offshore wind projects under development, and substantial deep and thick layers of subsurface halite suitable for storage facilities. This study develops a model of offshore wind generation, conversion to hydrogen, and subsurface storage in order to examine the feasibility of such a facility. Potential cavern locations and their theoretical storage capacities are determined using geological data of halite distribution. The model was applied to optimise the number, and locations, of caverns required. The cost of transmission of hydrogen by pipeline from offshore wind power-to-gas plants to storage caverns was shown to primarily depend on production volume and to a lesser extent on transmission distance. Following the application of constraints, a total of 218 potential caverns of height 120 m was identified in the Kish Basin. This corresponds to 23.68 TWh of energy storage capacity (as hydrogen), equivalent to up to 14.1% of Ireland's projected total electricity demand in 2050.